According to Importing Data
It is possible to import CI relationship data.
It states "To use this feature, you must have the DataIDs, SourceIDs, and TargetIDs of the configuration item records to link as well as the RecID of the CINamedRelConstraints record that defines the name of the relationship between the configuration items (such as "managed by" or "runs on")."
I have been unable to determine exactly what the DataID, SourceID and TargetID is.
I have tried using the CINamedRelConstaints RecID as the DataID, the parent Recd as the SourceID and child Recd as the TargetID to no avail.
Can anyone point me in the right direction?